Standard Weight (W s ) Equation and Length Categories for Shovelnose Sturgeon

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1 North Americn Journl of Fisheries Mngement 18:9 7, 18 Copyright by the Americn Fisheries Society 18 Stndrd Weight (W s ) Eqution nd Length Ctegories for Shovelnose Sturgeon MICHAEL C. QUIST,* CHRISTOPHER S. GUY, AND PATRICK J. BRAATEN Knss Coopertive Fish nd Wildlife Reserch Unit, 1 Division of Biology Knss Stte University, 205 Lesure Hll, Mnhttn, Knss 66506, USA Abstrct. Weight length dt were compiled from 32 popultions of shovelnose sturgeon Scphirhynchus pltorynchus (N 11,0) from nine sttes within the geogrphic distribution of the species. We used the regressionline-percentile technique, which provides 75th-percentile stndrd, to develop the stndrd weight (W s ) eqution. The proposed eqution in metric units is log 10 W s log 10 FL; W s is weight in grms nd FL is fork length in millimeters. The equivlent eqution in English units is log 10 W s log 10 FL; W s is weight in pounds nd FL is fork length in inches. These equtions re proposed for use with shovelnose sturgeon between 120 mm (5 in) nd 1,050 mm (41 in). Vlues for reltive weight (W r ) clculted with the W s eqution did not consistently increse or decrese with incresing fish length, indicting bsence of length bis. We propose the following length ctegories for clcultion of proportionl stock density (PSD) nd reltive stock densities (RSDs): stock, 250 mm (10 in); qulity, 380 mm (15 in); preferred, 510 mm (20 in); memorble, 640 mm (25 in); nd trophy, 810 mm (32 in). We found significnt reltions between size structure indices nd men popultion W r. Additionlly, we found significnt differences mong incrementl W r vlues. We believe the W s eqution nd length ctegory designtions will be useful tools for mnging shovelnose sturgeon popultions. Reltive weight [W r W/W s, where W is the observed weight nd W s is the length-specific stndrd weight vlue for the species; Wege nd Anderson (1978)] is commonly used s mngement tool to ssess the physiologicl well-being of fishes (i.e., condition). Reltive weight is esier to interpret thn the trditionl Fulton condition fctor (K), becuse unlike K, W r neither increses with incresing fish length nor vries by species. Thus, W r is useful when compring within nd mong fish popultions. Stock density indices re lso useful mngement tools to ssess fish popultions. Proportionl stock density [PSD (number of fish greter thn or equl to qulity length/number of fish greter * Corresponding uthor: mcquist@ksu.edu 1 The Unit is jointly supported by Knss Stte University, the Knss Deprtment of Wildlife nd Prks, the U.S. Geologicl Survey Biologicl Resources Division, nd the Wildlife Mngement Institute. thn or equl to stock length) ] nd reltive stock density [RSD (number of fish greter thn or equl to specified length/number of fish greter thn or equl to stock length) ] re commonly used to ssess size structure. However, before PSD or RSD cn be clculted for fish popultion, species-specific length ctegories must be defined. See Gbelhouse (1984) for methods to determine stock, qulity, preferred, memorble, nd trophy lengths. Despite the widespred use of W r nd stock density indices with wrmwter sportfish, W s equtions nd length ctegories re virtully nonexistent for lrge-river, nongme fishes. Therefore, the objectives of this study were to (1) develop W s eqution for shovelnose sturgeon Scphirhynchus pltorynchus bsed on the regression-line-percentile (RLP) technique, (2) evlute the consistency of W r cross vrious lengths, (3) evlute W r distributions of individuls nd popultions, (4) determine length ctegories (i.e., stock, qulity, preferred, memorble, nd trophy lengths), nd (5) ssess the reltions between W r nd size structure for shovelnose sturgeon popultions. Methods Weight length dt for shovelnose sturgeon were solicited from biologists within the geogrphicl distribution of the species (Lee et l. 1980). Popultions represented by less thn 30 individuls were omitted from ll nlyses. All dt were evluted s fork lengths (FL). One dt set submitted s totl lengths (TL) ws converted to fork length with n eqution developed from dt sets tht included both FL nd TL [FL (mm) (TL 43.14)/1.02; r 0., P ]. Additionlly, ll weights nd lengths were converted to grms nd millimeters. The RLP technique ws used to develop the W s eqution for shovelnose sturgeon (Murphy et l. 19). The minimum length for weight precision ws determined by plotting the vrince-to-men rtio by 1-cm length-groups, s suggested by Murphy et l. (19). Minimum length ws set where the vrince-to-men rtio exceeded pproximte- 9

2 MANAGEMENT BRIEFS 3 ly 0.01 (Neumnn nd Murphy 19). Minimum smple size for the ppliction of the RLP technique ws determined by methods described in Brown nd Murphy (16). Independence of W r cross length-clsses for ech study popultion ws evluted by ssessing the number of significnt positive nd negtive slopes of W r regressed on fish length. The totl number of significnt positive nd negtive slopes were compred with binomil test to detect ny length-relted bis in the W s eqution (Meht nd Ptel 19). Length ctegories were determined by methods described by Gbelhouse (1984). He suggested tht minimum stock, qulity, preferred, memorble, nd trophy lengths be determined from lengths encompssed by 20 26%, 36 41%, 45 55%, 59 64%, nd 74 80% of world record length, respectively. We used the lrgest fish in our dt set (1,052 mm FL; 8,164 g) s the world record length becuse the lrgest shovelnose sturgeon recorded by the Ntionl Freshwter Fishing Hll of Fme weighed 2,155 g. Severl uthors hve noted sesonl vritions in stock density indices (Crline et l. 1984; Serns 1985; Willis et l. 13). However, nerly ll dt sets represented summer or erly fll smpling, which mde seprtion by seson imprcticl. Similrly, size-relted bises cn result from ger selectivity (Hmley 1975; Reynolds nd Simpson 1978). Reltions between W r nd size structure were determined for those popultions known to be smpled with gill or trmmel nets from riverine hbitts. Men W r ws plotted s function of PSD nd s function of incrementl W r nd RSDs [i.e., stock to qulity (S Q), qulity to preferred (Q P), preferred to memorble (P M), nd memorble to trophy length (M T)]. The reltionships were nlyzed with correltion techniques. Differences of W r mong length ctegories were tested with nlysis of vrince (ANOVA; SAS 19). A probbility level of 0.05 ws used to reject the null hypothesis in ll sttisticl tests. Results nd Discussion Weight length regressions were developed for 32 shovelnose sturgeon popultions from nine sttes (N 11,0; Tble 1). We found tht 30 popultions were required to develop W s eqution with the RLP technique (smple vrince of slopes ; Michel L. Brown, South Dkot Stte University, personl communiction). Shovelnose sturgeon 120 mm nd longer were included in the weight length regressions becuse the vrince-to-men rtio ws below 0.01 for ll fish used. All weight length regressions were significnt (P ), nd ll but three correltion coefficients were 0.93 or higher (Tble 1). The following W s eqution for shovelnose sturgeon ws clculted with the 75th-percentile RLP technique: log W log FL; 10 s 10 where W s is stndrd weight in grms nd FL is in millimeters. The equivlent in English units is log W log FL; 10 s 10 where W s is stndrd weight in pounds nd FL is in inches. These equtions re proposed for use with shovelnose sturgeon from 120 mm (5 in) to 1,050 mm (41 in). Although W r my vry mong lengths in given popultion, there should be no consistent pttern of incresing or decresing W r vlues for series of popultions. When W r ws regressed on fish length for 32 popultions, 20 popultions hd significnt slopes (P 0.05). The number of positive slopes (11 slopes) ws not significntly different thn the number of negtive slopes (9 slopes; P 0.41), indicting no length bis ssocited with the W s eqution. Forty-three percent of the popultions hd men W r vlues within the suggested benchmrk trget rnge of (Wege nd Anderson 1978). Although this is similr to those percentges reported for white bss Morone chrysops (37%), plmetto bss ( hybrid of femle striped bss Morone sxtilis mle white bss; 32%; Brown nd Murphy 19), nd white crppie Pomoxis nnulris (Neumnn nd Murphy 19), 85% of these popultions were from Montn. Sixty percent of the Montn popultions hd men popultion W r vlues between nd 105. Conversely, 66% of the shovelnose sturgeon popultions from sttes other thn Montn hd men popultion W r vlues between 80 nd. These dt suggest tht universl trget vlues my be inpproprite for shovelnose sturgeon. Numerous reserchers hve described differences in W r vlues ssocited with lentic nd lotic popultions (e.g., Fisher et l. 16); however, we re unwre of ny studies identifying vrition in W r long longitudinl scle in lotic ecosystems. The vribility between lentic nd lotic systems hs prompted the development of differing trget rnges for W r. For exmple, Fisher et l. (16) found tht W r vlues for burbot Lot lot were consistently lower in lotic ecosystems thn in len-

3 4 QUIST ET AL. TABLE 1. Smple size (N; fish 120 mm), intercept (), slope (b), nd correltion coefficient (r) for regressions of log 10 weight (g) on log 10 fork length (mm). Men reltive weight (W r ) vlues for shovelnose sturgeon length ctegories (stock to qulity, S Q; qulity to preferred, Q P; preferred to memorble, P M; nd memorble to trophy, M T) re provided. Numbers in prentheses below the men re smple size nd SD of men. All regressions were significnt t P Illinois, Missouri Mississippi River, Pool 26 Mississippi River, Cpe Girrdeu Iow, Illinois Mississippi River, Pool 13 Stte nd loction N b r (15, 32.17) (15, 21.38) (5, 10.66) Knss Knss River, Lwrence (11, 10.97) Knss River, Ogden Knss, Missouri Missouri River, St. Joseph Missouri River, Knss City (5, 7.29) Louisin Red River Montn Big Muddy River (14, 20.44) Men W r vlues for length ctegories: S Q Q P P M M T (23, 23.17) 86 (50, 8.55) 83 (29, 5.94) (24, 6.81) 80 (13, 7.42) 81 (8, 4.88) 106 (8, 23.87) 58 (6, 14.19) 96 (25, 32.16) (80, 9.50) 84 (80, 6.88) 84 (206, 6.81) 78 (21, 11.93) (23, 6.52) (27, 10.70) (8, 20.65) 98 (14, 13.19) (9, 7.60) (47, 13.16) (212, 11.02) (74, 8.01) Mris River (36, 12.20) Missouri River, Lom 1, (49, 16.00) 106 (5, 12.33) Missouri River, Whiteside (11, 8.61) 98 (5, 3.56) 108 (37, 12.) Missouri River, Stfford Ferry (27, 10.59) 97 (51, 12.79) 103 (256, 11.04) Missouri River, Robinson Bridge 1, (16, 14.54) (85, 1.32) 107 (5, 14.45) 102 (1,004, 11.19) Missouri River, Fort Peck (11, 7.66) 93 (454, 9.00) (262, 9.17) Missouri River, Milk River confluence (12, 5.81) 88 (108, 7.52) 83 (46, 7.) Missouri River, Wolf Point (25, 9.28) 84 (73, 8.35) (14, 8.63) Missouri River, Red Wter River confluence (5, 8.11) Missouri nd Yellowstone River confluence (15, ) (61, 10.94) 98 (484, 11.55) (188, 10.11) Powder River (54, 8.) Tongue River Yellowstone River, Highwy 23 bridge (21, 11.) (48, 11.81) Yellowstone River, Forsyth (12, 7.05) Yellowstone River, Miles City (8, 10.11) Yellowstone River, Powder River confluence (37, 9.35) Yellowstone River, Glendive (7, 7.74) (29, 14.64) (123, 7.67) (178, 10.59) (55, 10.49) (101, 11.73) 96 (36, 9.85) (400, 11.07) (501, 11.23)

4 MANAGEMENT BRIEFS 9 TABLE 1. Continued. Stte nd loction N b r Yellowstone River, bove Intke (6, 18.86) Yellowstone River, 1, below Intke (29, 18.44) (, 10.86) Nebrsk Pltte River (13, 12.09) Men W r vlues for length ctegories: S Q Q P P M M T (60, 11.25) (337, 8.27) 87 (97, 7.) North Dkot Lke Ohe (38, 9.41) Lke Skkwe (15, 21.00) (23, 23.17) Wisconsin Chippew River 1, Represents less thn five individuls. (12, 6.21) (522, 8.09) 101 (334, 10.39) (5, 9.67) (7, 3.83) 69 (53, 8.56) 78 (21, 11.19) 83 (562, 7.84) FIGURE 1. Reltionship between men popultion reltive weight of memorble length to trophy length (W r M T) nd reltive stock density of memorble length to trophy length (RSD M T) for shovelnose sturgeon. tic ecosystems. Consequently, they suggested trget vlues of 105 for lentic popultions nd for lotic ecosystems. Kruse nd Hubert (17) found similr reltions with cutthrot trout Oncorhynchus clrki but elected to develop seprte equtions for lotic nd lentic popultions rther thn propose different trget vlues. Similrly, Willis et l. (19) identified brod distribution in body condition of yellow perch Perc flvescens nd suggested tht the vribility in condition reinforces the concept tht universl trget vlues my be inpproprite in mny situtions. Therefore, we suggest trget vlues of 105 for Montn popultions nd 80 for other popultions of shovelnose sturgeon. We recommend the following length ctegories be used when clculting stock density indices for shovelnose sturgeon: stock, 250 mm (10 in); qulity, 380 mm (15 in); preferred, 510 mm (20 in); memorble, 640 mm (25 in); nd trophy, 810 mm (32 in). All popultions hd PSD vlues greter thn 79, except for Mississippi River popultion (Tble 1). The number of popultions with high PSD vlues is not surprising becuse shovelnose sturgeon re typiclly collected with lrge-mesh (250-mm-br-mesure) nets. The primry gers used to smple shovelnose sturgeon for this study were either gill or trmmel nets. Thus, stock-length to qulity-length shovelnose sturgeon were less likely to be smpled. Stock density indices re used to quntify size structure of fish popultion. It is debtble whether such indices reflect growth, mortlity, nd recruitment. However, Willis (19) nd Guy nd Willis (19) documented reltions between PSD nd growth. Gbelhouse (1984) suggested tht low PSD vlues my reflect poor hbitt, overhrvest, nd reduced food supply. The reltion between PSD nd W r ginst growth re probbly one of cuse nd effect (Willis 19; Gbelhouse 19; Guy nd Willis 19). We were unble to

5 6 QUIST ET AL. P M nd M T fish (P 0.05; Figure 2). These dt illustrte the importnce of size-specific W r nlyses. Although the reltion between PSD nd W r probbly will vry with growth, we surmise tht these indices will be useful in ssessing shovelnose sturgeon size structure nd condition. At best, these indices will provide informtion on growth, mortlity, nd recruitment of shovelnose sturgeon in lrge-river ecosystems. We encourge fisheries biologists to develop W s equtions nd size structure ctegories for lrge-river species so tht these tools will be vilble for condition nd size structure ssessment. FIGURE 2. Reltions between men reltive weight (W r ) by length ctegory stock to qulity (S Q), qulity to preferred (Q P), preferred to memorble (P M), nd memorble to trophy (M T) for shovelnose sturgeon. Brs represent SE. Dt points without letter in common represent significnt differences ( 0.05) mong length ctegories. obtin growth dt for shovelnose sturgeon used in the development of the W s eqution. Thus, we used reltions between W r nd PSD to evlute the utility of these mngement tools for lrge-river species. Men popultion W r vlues were positively correlted (r 0.47, P 0.033) with PSD with curviliner regression model. Thus, popultions with higher PSD vlues hd higher men condition vlues. Similr results hve been reported for other species, such s northern pike Esox lucius (Willis nd Sclet 19), crppies Pomoxis spp. (Gbelhouse 1984b; Guy nd Willis 19), nd brook trout Slvelinus fontinlis (Johnson et l. 19). We lso plotted reltions between incrementl RSD nd W r. The best reltionship occurred between W r of M T nd RSD of M T (r 0.68, P ; Figure 1). In ddition, we found differences mong incrementl W r vlues. Men W r generlly decresed s fish ttined greter lengths. Stock-length to qulity-length shovelnose sturgeon hd significntly greter W r vlues thn Acknowledgments We thnk the following individuls for contributing the dt sets used in this project: Kenneth Bckes, Mel Bowler, Lyle Christensen, Rndy Clrmunt, Dvid Dy, Bill Grdner, Doug Henley, Robin Hofpr, Edwrd Peters, Greg Power, Bobby Reed, Mike Ruggles, Anne Tews, nd Gry Tilyou. In ddition, we thnk Mike Brown for sttisticl ssistnce. The U.S. Army, Deprtment of Defense nd Knss Stte University, Division of Biology, provided funding for this project. References Brown, M. L., nd B. R. Murphy. 19. Stndrd weights (W s ) for striped bss, white bss, nd hybrid striped bss. North Americn Journl of Fisheries Mngement 11: Brown, M. L., nd B. R. Murphy. 16. Selection of minimum smple size for ppliction of the regression-line-percentile technique. North Americn Journl of Fisheries Mngement 16: Crline, R. F., B. L. Johnson, nd T. J. Hll Estimtion nd interprettion of proportionl stock density for fish popultions in Ohio impoundments. North Americn Journl of Fisheries Mngement 4: Fisher, S. J., D. W. Willis, nd K. L. Pope. 16. An ssessment of burbot (Lot lot) weight length dt from North Americn popultions. Cndin Journl of Zoology 74: Gbelhouse, D. W., Jr A length-ctegoriztion system to ssess fish stocks. North Americn Journl of Fisheries Mngement 4: Gbelhouse, D. W., Jr. 1984b. An ssessment of crppie stocks in smll midwestern privte impoundments. North Americn Journl of Fisheries Mngement 4: Gbelhouse, D. W., Jr. 19. Sesonl chnges in body condition of white crppie nd reltions to growth in Melvern Reservoir, Knss. North Americn Journl of Fisheries Mngement 11: Guy, C. S., nd D. W. Willis. 19. Popultion chrcteristics of blck crppies in South Dkot wters:

6 MANAGEMENT BRIEFS 7 cse for ecosystem-specific mngement. North Americn Journl of Fisheries Mngement 15: Hmley, J. M Review of gill net selectivity. Journl of the Fisheries Reserch Bord of Cnd 32: Johnson, S. L., F. J. Rhel, nd W. A. Hubert. 19. Fctors influencing the size structure of brook trout popultions in bever ponds in Wyoming. North Americn Journl of Fisheries Mngement 12: Kruse, C. G., nd W. A. Hubert. 17. Proposed stndrd weight (W s ) equtions for interior cutthrot trout. North Americn Journl of Fisheries Mngement 17: Lee, D. S., nd five couthors Atls of North Americn freshwter fishes. North Crolin Museum of Nturl History, Rleigh. Meht, C., nd N. Ptel. 19. SttXct 3 for Windows, sttisticl softwre for exct nonprmetric inference, user mnul. CYTEL Softwre, Cmbridge, Msschusetts. Murphy, B. R., M. L. Brown, nd T. A. Springer. 19. Evlution of the reltive weight index, with new pplictions to wlleye. North Americn Journl of Fisheries Mngement 10: Murphy, B. R., D. W. Willis, nd T. A. Springer. 19. The reltive weight index in fisheries mngement: sttus nd needs. Fisheries 16(2): Neumnn, R. M., nd B. R. Murphy. 19. Evlution of the reltive weight (W r ) index for ssessment of white crppie nd blck crppie popultions. North Americn Journl of Fisheries Mngement 11: Reynolds, J. B., nd D. E. Simpson Evlution of fish smpling methods nd rotenone census. Pges in G. D. Novinger nd J. G. Dillrd, editors. New pproches to the mngement of smll impoundments. Americn Fisheries Society, North Centrl Division, Specil Publiction 5, Bethesd, Mrylnd. SAS Institute. 19. SAS procedures guide for personl computers, version SAS Institute, Cry, North Crolin. Serns, S. L Proportionl stock density index is it useful tool for ssessing fish popultions in northern ltitudes? Wisconsin Deprtment of Nturl Resources, Reserch Report 132, Mdison. Wege, G. J., nd R. O. Anderson Reltive weight (W r ): new index of condition for lrgemouth bss. Pges 79 in G. D. Novinger nd J. G. Dillrd, editors. New pproches to the mngement of smll impoundments. Americn Fisheries Society, North Centrl Division, Specil Publiction 5, Bethesd, Mrylnd. Willis, D. W. 19. A proposed stndrd length weight eqution for northern pike. North Americn Journl of Fisheries Mngement 9: Willis, D. W., C. S. Guy, nd B. R. Murphy. 19. Development nd evlution of stndrd weight (W s ) eqution for yellow perch. North Americn Journl of Fisheries Mngement 11: Willis, D. W., B. R. Murphy, nd C. S. Guy. 13. Stock density indices: development, use, nd limittions. Reviews in Fisheries Science 1: Willis, D. W., nd C. G. Sclet. 19. Reltions between proportionl stock density nd growth nd condition of northern pike popultions. North Americn Journl of Fisheries Mngement 9: Received Jnury 19, 18 Accepted April 21, 18